US 6268804 B1 Abstract A system for monitoring operation and location of a first moving vehicle relative to a second moving vehicle. A minimum separation distance between the first and second vehicles is estimated, based on the first vehicle velocity, and optionally on the second vehicle velocity, using location determination (LD) signals received from satellite-based transmitters from GPS, GLONASS and LEO satellites, or from ground-based signal sources such as LORAN signal towers, and using ranging signals from SONAR, RADAR or a similar system. The minimum separation distance is compared with the actual separation distance at selected times, and a vehicle driver is advised if the actual separation distance is too small, if the separation distance is decreasing too quickly, or if the second vehicle velocity is decreasing too quickly. The second vehicle may travel in the same traffic lane, in an adjacent lane, or on a road that intersects the road used by the first vehicle. Where the first and second vehicles travel on separate roads that will intersect, the system estimates whether the second vehicle will stop, or will be able to stop, at the intersection. The second vehicle may be a railroad car, such as a locomotive, or a road vehicle. A maximum vehicle clear-view velocity, consistent with vehicle stopping within a selected distance, is estimated. Road conditions are estimated and compensated for in estimating the minimum separation distance and/or the maximum vehicle clear-view velocity.
Claims(28) 1. A method of monitoring operation of a first moving vehicle relative to a second moving vehicle on a road, the method comprising the steps of:
estimating the present velocity of said first moving vehicle using location determination (LD) signals received from two or more LD signal sources;
estimating a separation distance between said first and second moving vehicles, said second moving vehicle adjacent to and moving in the same general direction as said first moving vehicle in a selected road lane, using ranging signals received from a ranging signal source;
estimating a minimum separation distance between said first moving vehicle and said second moving vehicle, said minimum separation distance based on said present velocity of said first moving vehicle;
comparing said separation distance and said minimum separation distance; and
providing a signal indicating that said separation distance between said first and second moving vehicles is less than said minimum separation distance, when said separation distance is no greater than said minimum separation distance;
providing a second signal indicating that s aid separation distance between said first and second moving vehicles will ultimately become less than said minimum separation distance when said separation distance is greater than said minimum separation distance and said separation distance while initially negative is becoming more positive at a greater than a selected threshold rate with respect to time.
2. The method of claim
1, wherein said step of estimating said minimum separation distance comprises the steps of:estimating a braking distance required to bring said first moving vehicle to a stop from said present velocity;
estimating a driver perception-reaction time;
estimating a driver perception-reaction distance by multiplying the driver perception-reaction time by said present velocity of said first vehicle; and
including the sum of the estimated braking distance and the estimated driver perception-reaction distance in said minimum separation distance for said first vehicle.
3. The method of claim
2, wherein said step of estimating said minimum separation distance further comprises the steps of:estimating a road condition of said road, where said road condition is drawn from a class of conditions comprising dry road pavement, slightly wet road pavement, totally wetted road pavement, ice present on the road pavement, and snow present on the road pavement; and
compensating in said estimation of said braking distance for said road condition.
4. The method of claim
3, wherein said step of compensating for said road condition comprises;estimating said braking distance for said dry road pavement; and
when said road condition is not said dry road pavement, increasing said braking distance by a selected fraction of said braking distance for said dry road pavement, where said fraction depends upon said road condition.
5. The method of claim
1, wherein said step of estimating said minimum separation distance comprises the steps of:estimating a rate, dependent upon said present velocity, at which said present velocity will decrease when a braking action is applied to said first moving vehicle; and
estimating said minimum separation distance as the distance required to bring said first moving vehicle to a stop after said braking action is first applied to said first moving vehicle based upon said rate.
6. A method of monitoring operation of a first moving vehicle relative to a second moving vehicle on a road, the method comprising the steps of:
estimating a first present velocity of said first moving vehicle using location determination (LD)signals received from two or more LD signal sources;
estimating a second present velocity of a second moving vehicle that moves in the same general direction as said first moving vehicle using ranging signals received from a ranging signal source;
estimating a separation distance between said first moving vehicle and said second moving vehicle using said ranging signals;
estimating a minimum separation distance between said first moving vehicle and said second moving vehicle, said minimum separation distance based on said first and second present velocities;
comparing said separation distance and said minimum separation distance; and
providing a signal indicating that said separation distance between said first and second moving vehicles is less than said minimum separation distance, when said separation distance is no greater than said minimum separation distance;
providing a second signal indicating that said separation distance between said first and second moving vehicles will ultimately become less than said minimum separation distance when said separation distance is greater than said minimum separation distance and said separation distance while initially negative is becoming more positive at a greater than a selected threshold rate with respect to time.
7. The method of claim
6, wherein said step of estimating said minimum separation distance comprises the steps of:estimating a first driver perception-reaction time;
estimating a first driver perception-reaction distance by multiplying said first driver perception-reaction time by said first present velocity;
estimating a first braking distance required to bring said first moving vehicle to a stop from said first present velocity;
estimating a second braking distance required to bring said second moving vehicle to a stop from said said present velocity; and
computing the difference of said first driver perception-reaction distance plus said first braking distance minus said second braking distance, and interpreting this difference as said minimum separation distance.
8. The method of claim
7, wherein said step of estimating said minimum separation distance further comprises the steps of:estimating a first rate, dependent upon said first present velocity, at which said first present velocity will decrease when a first braking action is applied to said first moving vehicle;
estimating said second rate, dependent upon said second present velocity, at which said second present velocity will decrease when a second braking action is applied to said second moving vehicle;
estimating said first braking distance required to bring said first moving vehicle to a stop after said first braking action is first applied to said first moving vehicle, based upon said first rate;
estimating a second braking distance required to bring said second moving vehicle to a stop after said second braking action is first applied to said second moving vehicle, based upon said second rate; and
estimating said minimum separation distance as the sum of said first driver perception-reaction distance plus said first braking distance minus said second braking distance.
9. The method of claim
6, wherein said step of estimating said minimum separation distance further comprises the steps of;estimating a road condition of said road, where said road condition is drawn from a class of conditions comprising dry road pavement, slightly wet road pavement, totally wetted road pavement, ice present on the road pavement, and snow present on the road pavement; and
compensating in at least one of said estimation of said first braking distance and said second braking distance for said road condition.
10. The method of claim
9, wherein said step of compensating for said road condition comprises:estimating said first braking distance and said second braking distance for said dry road pavement; and
when said road condition is not said dry road pavement, increasing at least one of said first braking distance and said second braking distance by a selected fraction of said respective first and second braking distances for said dry road pavement, where said fraction depends upon said condition.
11. The method of claim
6, further comprising the steps of:estimating a deceleration rate of said second moving vehicle;
comparing said deceleration rate with a selected threshold deceleration rate; and
providing a third signal indicating that said second vehicle is decelerating rapidly when the deceleration rate is less than said selected threshold deceleration rate.
12. A system for monitoring operation of a first moving vehicle relative to a second moving vehicle on a road, the system comprising:
a location determination (LD) module, carried on said first moving vehicle, that receives LD signals from at least two LD signal sources and estimates a present location and present velocity of said first moving vehicle and a separation distance between said first moving vehicle and said second moving vehicle that precedes and moves in the same general direction as said first moving vehicle;
a computer, connected to or a part of said LD module, that is programmed to:
estimate a minimum separation distance between said first and second moving vehicles; and
compare said separation distance and said minimum separation distance; and
a display that provides a signal, in at least one of visually perceptible form and audibly perceptible form, indicating that said separation distance between said first and second moving vehicles is less than said minimum separation distance, when said separation distance is no greater than said minimum separation distance;
wherein said computer is programmed to cause said display to provide a second signal indicating that said separation distance between said first and second moving vehicles will ultimately become less than said minimum separation distance when said separation distance is greater than said minimum separation distance, but the difference between said minimum separation distance and said separation distance while initially negative is becoming more positive at greater than a selected threshold rate with respect to time.
13. The system of claim
12, wherein said computer estimates said minimum separation distance by including the steps of:estimating a braking distance required to bring said first moving vehicle to a stop from said present velocity;
estimating a driver perception-reaction time;
estimating a driver perception-reaction distance by multiplying said driver perception-reaction time by said present velocity of said first vehicle; and
including the sum of said estimated braking distance and the estimated driver perception-reaction distance in said minimum separation distance for said first moving vehicle.
14. The system of claim
13, wherein said computer estimates said minimum separation distance by including the further steps of:estimating a road condition of said road, where said road condition is drawn from a class of conditions comprising dry road pavement, slightly wet road pavement, totally wetted road pavement, ice present on the road pavement, and snow present on the road pavement; and
compensating in said estimation of said braking distance for said road condition.
15. The system of claim
14, wherein said computer compensates for said road condition by including the steps of:estimating said braking distance for said dry road pavement; and
when said road condition is not said dry road pavement, causing said computer to increase said braking distance by a selected fraction of said braking distance for said dry road pavement, where said fraction depends upon said road condition.
16. The system of claim
15, further comprising a road pavement sensor, connected to said computer, that:examines a selected portion of road pavement adjacent to said first moving vehicle as said first moving vehicle moves along said road pavement; and
estimates whether said selected portion of said road pavement is dry, slightly wet, wet, substantially covered with ice or substantially covered with snow.
17. The system of claim
12, wherein said computer estimates said minimum separation distance by including the steps of:estimating a rate, dependent upon said present velocity, at which said present velocity will decrease when a braking action is applied to said first moving vehicle; and
estimating said minimum separation distance as the distance required to bring said first moving vehicle to a stop after said braking action is first applied to said first moving vehicle, based upon said rate.
18. The system of claim
12, wherein said computer is installed in said first moving vehicle and performs at least one function that is not related to monitoring said separation distance and said minimum separation distance.19. The system of claim
12, wherein said system includes a data/command entry module, connected to said computer, that allows entry of at least one of an item of data and a command for said system to perform a selected task related to monitoring said separation distance and said minimum separation distance.20. The systems of claim
12, further comprising at least one of the following, connected to said computer:a CD ROM player, carried on said first moving vehicle;
a radio receiver that receives at least one of AM signals and FM signals, carried on said first moving vehicle;
a fuel usage monitor, carried on said first moving vehicle; and
a temperature monitor carried on said first moving vehicle.
21. The system of claim
12, wherein said first moving vehicle has a dashboard and at least one of said LD module, said computer, and said display is installed in said dashboard.22. A system for monitoring operation of a first moving vehicle relative to a second moving vehicle on a road, the system comprising:
a location determination (LD) module, carried on a first moving vehicle, that receives LD signals from at least two LD signal sources and estimates a first resent location and a first present velocity of said first vehicle;
a ranging signal source located on said LD module that transmits and receives ranging signals to estimate a second present location and second present velocity v(t;
2) of said second moving vehicle that precedes and moves in the same general direction as said first moving vehicle, and a separation distance between said first moving vehicle and said second moving vehicle; a computer, connected to or a part of said LD module, that is programmed to:
estimate a minimum separation distance between said first and moving vehicles; and
compare said separation distance and said minimum separation distance; and
a display that provides a signal, in at least one of visually perceptible form and audibly perceptible form, indicating that said separation distance between said first and second moving vehicles is less than said minimum separation distance, when said separation distance is no greater than said minimum separation distance;
wherein said computer is programmed to cause said display to provide a second signal indicating that said separation distance between said first and second moving vehicles will ultimately become less than said minimum separation distance when said separation distance is greater than said minimum separation distance, but the difference between said minimum separation distance and said separation distance while initially negative is becoming more positive at greater than a selected threshold rate with respect to time.
23. The system of claim
22, wherein said computer estimates said minimum separation distance by including the steps of:estimating a first driver perception-reaction time;
estimating a first driver perception-reaction distance by multiplying said first driver perception-reaction time by said first resent velocity;
estimating a first braking distance required to bring said first moving vehicle to a stop from said first present velocity;
estimating a second braking distance required to bring said second moving vehicle to a stop from said second present velocity; and
computing the difference of said first driver perception-reaction distance plus said first braking distance minus said second braking distance, and interpreting this difference as said minimum separation distance.
24. The system of claim
23, wherein said computer further estimates said minimum separation distance by including the steps of:estimating a first rate, dependent upon said first present velocity, at which said first present velocity will decrease when a first braking action is applied to said first moving vehicle.
estimating a second rate, dependent upon said second present velocity, at which said second present velocity will decrease when a second braking action is applied to said second moving vehicle;
estimating said first braking distance required to bring said first moving vehicle to a stop after said first braking action is first applied to said first moving vehicle, based upon said first rate;
estimating said second braking distance required to bring said second moving vehicle to a stop after said second braking action is first applied to said second moving vehicle, based upon said second rate; and
estimating said minimum separation distance as the sum of said first driver perception-reaction distance plus said first braking distance minus said second braking distance.
25. The system of claim
23, wherein said computer estimates said minimum separation distance by including the steps of:compensating in at least one of said estimation of said first braking distance and said second braking distance for said road condition.
26. The system of claim
25, wherein said computer compensates for said road condition by including the steps of:estimating said first braking distance and said second braking distance for said dry road pavement; and
when said road condition is not said dry road pavement, increasing at least one of said first braking distance and said second braking distance by a selected fraction of said respective first and second braking distances for said dry road pavement, where said fraction depends upon said road condition.
27. The system of claim
22, wherein said computer is further programmed to:estimate a deceleration rate of said second moving vehicle;
comparing said deceleration rate with a selected threshold deceleration rate; and
providing a signal indicating that said second vehicle is decelerating rapidly when the deceleration rate is less than said selected threshold deceleration rate.
28. The system of claim
22, wherein said first moving vehicle has a dashboard and at least one of said LD module, said computer, and said display is installed in said dashboard.Description This is a divisional of application Ser. No. 08/993,693 filed on Dec. 18, 1997, now U.S. Pat. No. 6,067,031. This invention relates to dynamic monitoring of a separation zone surrounding a moving vehicle, from which other vehicles are to be excluded. A moving vehicle, such as an automobile, truck, bus, motorcycle or railroad car, requires at least a minimum braking distance to stop after vehicle brakes are applied and an additional time and equivalent perception-reaction distance for the vehicle driver to perceive and/or react and to apply the brakes. Each of the braking distance and the perception-reaction distance increases with vehicle velocity and may be different for different vehicles and for different drivers. Where a first vehicle immediately follows a second vehicle in a traffic lane on a highway, expressway, street, lane or road (“road”), safe operation of the first vehicle requires keeping some distance between the first and second vehicles. Many drivers use an approximately fixed separation distance from the preceding vehicle, and this distance (often as small as two vehicle lengths) does not vary with vehicle velocity, with the type of vehicle, with road conditions or with the driver. Monitoring of vehicle velocities, vehicle spacings and the like, that control access to a specified zone, is disclosed in several U.S. patents. Most of these patents do not concern separation of two consecutive vehicles with reference to the individual velocities of the two vehicles. What is needed is a system for creating and subsequently monitoring a variable vehicle-to-vehicle buffer zone or separation distance whose location moves with the vehicle and whose size and/or character can change with vehicle velocities, with road conditions and with other variables. Preferably, the system should determine and take account of the velocities of each of the two vehicles and should permit receipt of information, received from a central station or elsewhere, that may affect determination of the size of the vehicle buffer zone. These needs are met by the invention, which provides a system that uses location determination (LD) signals, ranging signals, road condition information and other information, received at the monitored vehicle, (1) to determine the present location and present velocity of the monitored vehicle and of the immediately preceding vehicle in the same road lane, (2) to determine a suitable minimum vehicle-to-vehicle separation distance for two vehicles traveling in the same road lane and to optionally display this distance, visually or audibly, to the driver, (3) to compare the minimum separation distance with the actual separation distance and to advise the driver if the monitored vehicle is too close to the immediately preceding vehicle, (4) to determine a maximum clear-view vehicle velocity, and (5) to take account of road conditions and other changing circumstances that may alter the minimum separation distance or maximum clear-view velocity. The monitored vehicle carries, or has attached thereto, an LD module that receives LD signals and estimates the present location and velocity of the LD module and that estimates the present location and present velocity of a vehicle, if any, that immediately precedes the monitored vehicle in the same road lane and moves in the same direction. The LD module may include a communications module that exchanges information with a central station. FIGS. 1 and 3 illustrate practice of the invention in two embodiments. FIG. 2 is a schematic view of apparatus for practicing the invention. FIGS. 4, FIGS. 7 and 9 illustrate apparatus for determining vehicle road conditions. FIG. 8 graphically illustrates reflectivity versus road conditions. The present invention hereby incorporates herein by reference the related application by the same inventors titled “Dynamic Monitoring of Vehicle Separation”, filed with the U.S. Patent and Trademark Office on Dec. 18, 1997 as U.S. patent application No. 08/993,693, and issued on May 23, 2000 as U.S. Pat. No. 6,067,031. FIG. 1 illustrates one situation for practice of the invention. A monitored or first vehicle Optionally, the communications, control and display functionalities can be built into the vehicle The invention is used to determine and present a minimum separation distance d(t; FIG. 2 is a schematic view of an LD module The ranging module A preferred alternative for the ranging module Alternatively, a side-looking or conventional RADAR system can be used for a ranging module The LD module The LD module A visual display An audible display The LD module also includes a power module The supplementary service module The communications signals used by the transceiver Table 1 includes data taken from a Skid Chart compiled by Michael J. Shepston & Associates, Traffic Accident Reconstruction, Cave Creek, Ariz. 85331. Table 1 provides estimates of perception-reaction distance (conservatively assuming a driver perception-reaction time of 1.5 sec. at any velocity), braking distance and total stopping distance (sum of columns 2 and 3) for a passenger vehicle initially traveling at various velocities, as gathered and analyzed by various highway monitoring groups. The Total Stopping Distance set forth in Table 1 represents a suitable separation distance for two vehicles traveling in the same lane and in the same direction on dry pavement. The results set forth in Table 1 may be modified by taking account of road surface condition (dry, slightly wet, wet/saturated, snow, ice, sleet, etc.) on braking distance.
A general model for vehicle deceleration upon braking assumes that loss of vehicle velocity v is proportional to a pth power of velocity, viz.
where K′ and p are parameters that should be determined by measurement. Assuming that p≠+1 (a special case), this model has the following solutions for velocity and linear displacement.
If vehicle braking is applied at t=t
and the braking distance will be
If kinetic energy is assumed to be lost at a constant rate throughout the braking interval, p=−1 and the braking distance Δx(brake) is proportional to v Most tabular estimates of braking distance, including the results presented in Table 1, appear to incorporate the assumption that p=0. It is preferable, where possible, to estimate the value of the parameters p and K using measurements on a given vehicle. For example, if the braking distance Δx(brake;v
where a is any real number greater than 1.0, such as a=2, a=e≈2.718282 and a=10. Using this estimate, one can easily verify that p≈0 is assumed for the results presented in Table 1. These considerations can be used to provide an arguably more realistic determination of minimum separation distance, using knowledge of the velocities v(t;
From Eq. (2), the second vehicle
after traveling an additional braking distance
The first vehicle
after traveling an additional total stopping distance of
The difference
if non-negative, is the minimum separation distance that is appropriate for this situation. At any time t before the second vehicle
The parameters p and K for the first vehicle and for the second vehicle may differ. If the parameter p=0 for both vehicles, Eq. (15) becomes
Equation (13) or (14) may be implemented to provide adaptive cruise control for appropriate separation of the first vehicle The quantity d(t;
is non-negative, or if the difference Δ(t; ∂Δ( (i) the driver of the first vehicle In the unlikely event that the parameter p=+1, the solutions for velocity and linear displacement, analogous to Eqs. (2) and (4), become
The minimum separation distance d(t;
by analogy with Eq. (15). The formalism developed in Eqs. (1)-(7) can also be used to estimate when the second vehicle is decelerating rapidly without the second vehicle's brake light indicating such deceleration. A change in velocity of the second vehicle may be estimated by the relation
where the first term on the left is computed using the system's measurement of the separation distance d(t;
where ν The preceding formalism can also be used to estimate a maximum clear-view vehicle velocity v(t;D;max) that is consistent with stopping a vehicle within a selected clear-view stopping distance D, which may be a vehicle-to-vehicle separation distance or a representative visual distance where the vehicle is operated in heavy fog or under other inclement weather conditions that severely reduce visibility. Equation (13) may be re-expressed in the form
If the parameter p=0, corresponding to constant momentum loss during braking, Eq. (23) becomes a quadratic equation,
which has a solution
If the parameter p=−1, corresponding to constant loss of energy during braking, Eq. (23) becomes a cubic relation
which has at least one real root and is solvable analytically. If the parameter p has some value other than p=0 or p=1, the maximum velocity v(t;
FIG. 3 illustrates an alternative embodiment, in which a first range/range rate determination module or “ranging” module The second ranging module
where the bearing angle φ(t; After the closure rate ∂d(t;
The time derivative ∂Δx
V
V
and V
V
V
V The first, second and third velocity ranges set forth in Eqs. (33A), (33B) and (33C) may be changed modestly to reflect the particular circumstances of the situation represented in FIG. 3 for the first and third vehicles. Similarly, the first, second and third velocity ranges set forth in Eqs. (34A), (34B) and (34C) may be changed modestly to reflect the particular circumstances of the situation represented in FIG. 3 for the first and third vehicles. It is preferable that the first, second and third velocity ranges chosen for the variable ∂Δx The driver of the first vehicle The second ranging module The third ranging module
where the bearing angle φ(t;
The system refers to its electronic map whenever another vehicle or other object
where the velocity v(t;
and computes the heading angle Ψ(t;
If the quantity v(t;
or
Where the quantity v(t;
the system concludes that the fourth vehicle If v(t;
the system concludes that the fourth vehicle
the system concludes that the fourth vehicle does not have sufficient time to significantly slow down for, or stop at, the intersection The system then optionally estimates the time interval length Δt
where Δt(clear) is a selected time interval length, such as 1-3 sec. The system also optionally estimates the time interval length Δt
The system optionally computes Δt This last embodiment can also be applied to an intersection of a road FIG. 4 is a flow chart of a suitable procedure for implementing the vehicle-to-vehicle separation distance embodiment of the invention, using only the observed velocity v(t; FIG. 5 is a flow chart of a suitable procedure for implementing the vehicle-to-vehicle separation distance embodiment of the invention, using the observed velocities v(t; Because the first, second and third x-ranges are exhaustive and mutually exclusive, one of the steps FIG. 6 is a flow chart of a suitable procedure for implementing the vehicle-to-vehicle separation distance embodiment of the invention, using the observed velocities v(t; The system may also take account of the weather conditions and road conditions in which a vehicle operates. The preceding discussion will apply to a road that is dry or damp but may need to be modified for a road that is wet or is covered with snow or ice. For a road that is wet, snowy or icy, Eq. (1) may need to be modified, by adding a fraction f of the dry road stopping distance to the total distance required to bring the vehicle to a stop. For a snowy or icy road, this fraction f may be larger than 1 so that the stopping distance for such road conditions is more than twice the stopping distance for a dry road. If the fraction f can be measured or estimated, the stopping distance can be increased by the fraction f by reducing the coefficient K(dry road) in Eq. (1), for example, by replacing this coefficient by the coefficient
Use of a coefficient K(non-dry), as in Eq. (45), will increase the stopping distance of each of two consecutive vehicles and will increase the minimum stopping distance between the two vehicles. If the stopping distance for a wet, snowy or icy road cannot be modeled using a fractional increase relative to the dry road stopping distance, the non-dry stopping distance may need to be measured for different conditions and incorporated in an on-vehicle table. Local road conditions can be estimated by an optical, infrared or other road condition sensor The sensor
where the parameters RL(j) (j=1, 2, 3, 4) are selected numerical values that have been determined empirically for the type of road on which the vehicle now moves. The LD signal receiver/processor Preferably, the sensor FIG. 9 illustrates, in more detail, apparatus
and the ratio r(rcv) can be used as the reflected light value RL to estimate the road conditions as in Eqs. (46A)-(46D). Alternatively, an intensity difference
can be formed and used as the reflected light value RL to estimate the road conditions as in Eqs. (46A)-(46D). If heavy fog or another visibility-reducing atmosphere is present, the light sensor Presence of a visibility-reducing atmosphere should be distinguished from a situation in which the light beam source If the second light beam sensor Patent Citations
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